An optical waveguide is a field which has been actively studied in a next generation communication system for a fast transmission of massive information.
In order to manufacture a highly integrated optical waveguide, a process for manufacturing a planar optical waveguide has been actively studied. In order to find a solution for the highly integrated optical waveguide, a process for manufacturing a two-dimensional optical waveguide has been studied.
Among process techniques for manufacturing a planar optical waveguide, an imprinting process is a method for transcribing a pattern onto a polymer layer using a mold having a micro structure. A direct transcription technique of a pattern causes mass replication of a micro structure to be possible with a simple process, a short process time and a low process cost, thereby having a considerable advantage over the other processes.
A study for manufacturing a two-dimensional optical waveguide by the imprinting process is implemented by using two imprint molds. Specifically, according to the study for manufacturing a two-dimensional optical waveguide, a clad polymer layer is inserted between two imprint molds, and then an intermediate clad is manufactured.
Hereinafter, a process for manufacturing a planar optical waveguide will be described.
FIGS. 1 to 5 are sectional views of a process for manufacturing an optical waveguide using a conventional hot-embossing process.
A planar optical waveguide is generally manufactured by means of a photo lithography process.
The process for manufacturing an optical waveguide using a photo lithography process is composed of the steps of: (1) coating a silicon wafer of a quartz wafer with an adhesion promoter for enhancing an adhesion effect between a wafer and a polymer; (2) coating an upper surface of the adhesion promoter with a lower clad of a polymer resin once again and curing it; (3) coating the lower clad with a polymer core resin having a refractive index higher than that of the lower clad and curing it; (4) coating the polymer core resin with another photosensitive polymer (photoresist) and soft-baking it; (5) exposing the photoresist using a photo mask; (6) baking (post exposure baking) an exposed pattern in the photoresist; (7) developing the pattern of the photoresist and baking (hard baking) it; (8) etching a core layer using the photoresist as an etching mask; (9) removing the photoresist pattern remaining on the core pattern; and (10) manufacturing an upper clad of the same polymer resin as the lower clad on the core pattern.
A process for a more simplified process, a lower cost and shorter process steps to manufacture the same optical waveguide has been actively studied, and an imprinting process is one of the processes which have been in the limelight among others.
The imprinting process is composed of the steps of (1) manufacturing a lower clad on a polymer layer using a mold having a micro-pattern; (2) filling an inside of a pattern of the lower clad with a core; and (3) completing an optical waveguide by manufacturing an upper clad.
A detailed method for manufacturing an optical waveguide using an imprinting process will be illustrated with reference to FIGS. 1 to 5.
First of all, as shown in FIGS. 1 and 2, an imprint mold 11 is used to form a lower clad 12a having a core structure on a polymer layer 12.
At this time, the imprinting process for manufacturing the lower clad may be classified into a hot-embossing technique in which mobility of a polymer due to an increase in temperature is used to manufacture the lower clad, and an ultraviolet embossing technique in which an ultraviolet curable polymer is used to manufacture the lower clad.
Then, as shown in FIG. 3, the lower clad 12a and the imprint mold 11 are separated from each other.
As shown in FIG. 4, a core channel of the lower clad 12a is filled with a core resin 14, i.e., a polymer resin having a refractive index higher than that of the lower clad 12a. 
Then, as shown in FIG. 5, the upper clad 13 is stacked, and the core resin is cured by ultraviolet to complete the optical waveguide.
The method for manufacturing the optical waveguide as described above is a representative method for manufacturing an optical waveguide.
Hereinafter, a method for manufacturing a two-dimensional optical waveguide in connection with the method for manufacturing the optical waveguide as described above will be described as follows.
A method for manufacturing a two-dimensional polymer optical waveguide by a photolithography process sequentially repeats once more the method for manufacturing the optical waveguide as described above.
Accordingly, repetitive and complicated processes require a long process time.
In addition, a method for manufacturing a two-dimensional optical waveguide by an imprinting process is implemented through a study for various processes. Specifically, two imprint molds are used according to a study for manufacturing a two-dimensional optical waveguide, wherein a clad polymer layer is inserted between the two imprint molds and then an intermediate clad is manufactured.
However, the molds required in the imprinting process are manufactured of a material, such as silicon, nickel, quartz, or the like by a process of electron beam lithography or optical lithography.
Accordingly, there is a connotation of a limitation concerning a higher process cost for manufacturing an imprint mold.
In order to resolve the above-mentioned problem, a technique for manufacturing a two-dimensional optical waveguide in a simple manner and in a short process time using a single imprint mold has been urgently required.